Wubei Zhi (Vol. 48)

A?bove is the structure of the gate house, which serves as a resource for defensive equipment styles.

A woodblock illustration of a Chui Bei Dropping Stone Monument/Slab, a defensive military engine mounted atop a city gate. The illustration shows a fortified city wall with a large double-arched gate at the base. Above the gate, on the ramparts, is a two-story wooden pavilion structure. Suspended within this structure is a large, heavy rectangular board or stone-dropping device, studded with sharp iron spikes or teeth, designed to be dropped onto attackers attempting to breach the gate below. The device is held by ropes and pulleys attached to a horizontal beam.